Pellicle for photomask and method of fabricating the same

ABSTRACT

A pellicle for a photomask comprises a pellicle membrane. The pellicle membrane incudes a base layer having a first surface and a second surface facing the first surface, and a first recovery layer covering the first surface of the base layer. A content of SP2 covalent bonds between carbon atoms contained in the first recovery layer is less than or equal to a content of SP2 covalent bonds between carbon atoms contained in the base layer.

CROSS-REFERENCE TO RELATED APPLICATION

This U.S. nonprovisional application is a divisional of U.S. applicationSer. No. 16/214,781, filed on Dec. 10, 2018, which claims priority under35 U.S.C § 119 to Korean Patent Application No. 10-2018-0069205 filed onJun. 15, 2018 in the Korean Intellectual Property Office, the entirecontents of each of which are hereby incorporated by reference.

BACKGROUND

Inventive concepts relate to pellicles for photomasks and/or methods offabricating the same.

A pellicle for a photomask may be provided in the form of a film on aphotomask to protect the photomask from external contaminants (e.g.,dust, resist, and/or the like) during optical/EUV lithography. Apellicle for a photomask should have high transmittance with respect tolight used in a lithography process and other features such as heatradiation, strength, uniformity, durability, and stability. As linewidths of semiconductor devices and electronic circuits have beenreduced, a wavelength of light used for the lithography process becomesshorter and development of a suitable pellicle material based on a lightsource used for the lithography process is being pursued.

SUMMARY

Some example embodiments of inventive concepts provide pellicles forphotomasks, the pellicles having superior optical characteristics,durability, and mechanical strength.

Some example embodiments of inventive concepts provide methods offabricating pellicles for photomasks, the pellicles having superioroptical characteristics, durability, and mechanical strength.

According to some example embodiments of inventive concepts, a pelliclefor a photomask comprises a pellicle membrane. The pellicle membraneincudes a base layer having a first surface and a second surface facingthe first surface, and a first recovery layer covering the first surfaceof the base layer. A content of SP2 covalent bonds between carbon atomscontained in the first recovery layer is less than or equal to a contentof SP2 covalent bonds between carbon atoms contained in the base layer.

According to some example embodiments of inventive concepts, method offabricating a pellicle for a photomask includes providing a pelliclemembrane and transcribing the pellicle membrane onto a frame. Providingthe pellicle membrane includes forming a base layer having a firstsurface and a second surface facing the first surface, coating a firstcarbon-containing material on the first surface of the base layer, andperforming a first heat treatment process at a first process temperatureto form a first recovery layer that is bonded to the base layer. Thefirst carbon-containing material includes catecholamine.

According to some example embodiments of inventive concepts, a pelliclefor a photomask, the pellicle comprises a pellicle membrane. Thepellicle membrane includes a base layer that has a first surface and asecond surface facing the first surface, a first recovery layer thatcovers the first surface of the base layer, and a support layer thatcovers the second surface of the base layer. Each of the base layer, thefirst recovery layer, and the support layer contain carbon atoms. Acontent of SP2 covalent bonds between the carbon atoms contained in thefirst recovery layer is less than or equal to a content of SP2 covalentbonds between the carbon atoms contained in the base layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view showing a pellicle for aphotomask, according to some example embodiments of inventive concepts.

FIG. 2 illustrates an enlarged view showing section P1 of FIG. 1;

FIGS. 3 to 6 illustrate carbon bond structures of atomic layers atdifferent heights;

FIG. 7 illustrates a flow chart showing a method of fabricating apellicle for a photomask, according to some example embodiments ofinventive concepts;

FIGS. 8 and 10 illustrate cross-sectional views showing a method offabricating a pellicle for a photomask, according to some exampleembodiments of inventive concepts;

FIG. 9 illustrates an enlarged view showing section P2 of FIG. 8;

FIG. 11 illustrates an enlarged view showing section P3 of FIG. 10;

FIG. 12 illustrates a perspective view showing a step in a method offabricating a pellicle for a photomask, according to some exampleembodiments of inventive concepts;

FIG. 13A illustrates an optical image of a base layer manufacturedaccording to some example embodiments of inventive concepts;

FIG. 13B illustrates an optical image obtained after coatingcatecholamine on the base layer of FIG. 13A;

FIG. 13C illustrates an optical image obtained after forming a recoverylayer by thermally treating the catecholamine of FIG. 13B;

FIG. 14 illustrates a graph showing Raman spectrums of a defect-freegraphite layer and a pellicle membrane that is manufactured by a methodof fabricating a pellicle for a photomask, according to some exampleembodiments of inventive concepts;

FIG. 15 illustrates a cross-sectional view showing a pellicle for aphotomask, according to some example embodiments of inventive concepts.

FIG. 16 illustrates an enlarged view showing section P4 of FIG. 15;

FIGS. 17 to 19 and 21 to 23 illustrate cross-sectional views showing apellicle for a photomask, according to some example embodiments ofinventive concepts;

FIG. 20 illustrates an enlarged view showing section P5 of FIG. 19;

FIG. 24 illustrates a cross-sectional view showing a pellicle accordingto some example embodiments of inventive concepts; and

FIG. 25 illustrates a schematic diagram showing a photolithographyprocess that uses a reticle including a pellicle according to someexample embodiments of inventive concepts.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Some example embodiments of inventive concepts will now be described indetail with reference to the accompanying drawings to aid in clearlyexplaining inventive concepts.

When numerical values or equalities are used herein without any furthermodification, it is intended that the associated numerical value includea tolerance, e.g. an engineering tolerance, around the stated numericalvalue or equality that is known to one of ordinary skill in the art.When ranges are specified, the range includes all values therebetweensuch as increments of 0.1%.

FIG. 1 illustrates a cross-sectional view showing a pellicle for aphotomask, according to some example embodiments of inventive concepts.FIG. 2 illustrates an enlarged view showing section P1 of FIG. 1. FIGS.3 to 6 illustrate carbon bond structures of atomic layers at differentheights.

Referring to FIG. 1, a pellicle 50 for a photomask may include apellicle membrane 20 and a pellicle frame 30 attached to an edge of thepellicle membrane. The pellicle 50 may be applicable to, e.g. used in,an extreme ultraviolet (EUV) mask used for EUV lithography. The pelliclemembrane 20 may include a base layer 1 and a recovery layer 3. The baselayer 1 may have a first surface 1 a and a second surface 1 b facingeach other. The recovery layer 3 may be on the first surface 1 a of thebase layer 1. The pellicle frame 30 may be on the second surface 1 b ofthe base layer 1. The base layer 1 and the recovery layer 3 may allcontain carbon. The base layer 1 may be or may include, for example, atleast one of a graphene thin layer or a graphite thin layer. Therecovery layer 3 may have a similar structure to that of the base layer1. A bond structure between carbon atoms contained in the base layer 1may primarily include SP2 covalent bonds, which are planar bondstructures, and secondly include SP3 covalent bonds, which aretetrahedral bond structures. For example, in the base layer 1, a contentratio of the SP2 covalent bonds to the SP3 covalent bonds may be about70:30 to 90:10 or about 84:16 to 83:17. The pellicle frame 30 may have,for example, one of a regular square shape and a rectangular shape eachof which has two pairs of parallel sides. The pellicle frame 30 mayinclude a metal or an alloy of the metal, for example, aluminum, zinc,magnesium, stainless steel, molybdenum, zirconium, tungsten, or acombination thereof, or may be treated by anodizing or diamond-likecarbon (DLC) technology.

Referring to FIGS. 1 and 2, at least one pinhole or cavity 1 r may bepresent on the first surface 1 a of the base layer 1. The recovery layer3 may fill the pinhole 1 r, while covering the first surface 1 a of thebase layer 1. The recovery layer 3 may have an identical or similarstructure to that of graphene or graphite. A bond structure betweencarbon atoms contained in the recovery layer 3 may primarily include SP2covalent bonds, which are planar bond structures, and secondly includeSP3 covalent bonds, which are tetrahedral bond structures. Acontent/density of the SP2 covalent bonds between carbon atoms containedin the recovery layer 3 may be less than a content/density of the SP2covalent bonds between carbon atoms contained in the base layer 1. Therecovery layer 3 may include at least one of nitrogen, hydrogen, oroxygen, or a combination thereof, or a sub-combination thereof. Acontent/density of at least one of nitrogen, hydrogen, or oxygencontained in the recovery layer 3 may be greater than a content/densityof at least one of nitrogen, hydrogen, or oxygen contained in the baselayer 1.

The base layer 1 may be provided therein with base atomic layers Ala andAlm. The base atomic layers Ala and Alm may include first base atomiclayers Ala and second base atomic layers Alm spaced apart in a directioncorresponding to a C-axis direction from the first base atomic layersAla. The pinhole 1 r may be formed in the second base atomic layers Alm.The C-axis direction may be perpendicular to surfaces of the base atomiclayers Ala and Alm, or may be a thickness direction of the base layer 1.As shown in FIGS. 3 and 5, each of the base atomic layers Ala and Almmay include first carbon atoms C1 that form hexagonal structures.

The recovery layer 3 may be provided therein with recovery atomic layersCln spaced apart from each other in the C-axis direction. As shown inFIG. 4, each of the recovery atomic layers Cln may include second carbonatoms C2 that form hexagonal structures. Carbon bonds in the base atomiclayers Ala and Alm and the recovery atomic layers Cln may primarilyinclude SP2 covalent bonds that are oriented along a directionperpendicular to the C-axis direction. Carbon bonds in the base atomiclayers Ala and Alm and the recovery atomic layers Cln may slightlyinclude SP3 covalent bonds that are oriented along a direction parallelto the C-axis. A content/density of the SP3 covalent bonds betweencarbon atoms contained in the recovery layer 3 may be greater than acontent/density of the SP3 covalent bonds between carbon atoms containedin the base layer 1.

As shown in FIG. 5, the second base atomic layer Alm may include thepinhole 1 r that is a hollow area in which the first carbon atoms C1 areabsent. A sidewall of the pinhole 1 r may be provided thereon withdangling bonds DB and/or broken bonds of the first carbon atoms C1. Whenthe base layer 1 exclusive of the recovery layer 3 is used as a pelliclemembrane, the base layer 1 may suffer from damage such as partial lossof aperture caused by combination of the dangling bonds DB with gasessuch as hydrogen supplied in a photolithography process (e.g., causedwhen the first carbon atoms C1 are evaporated into methane (CH₄)).Accordingly, the damaged pellicle membrane may not protect a photomaskThe photomask may be attached with foreign substances, with the resultthat a photolithography process may not be reliably performed.

According to inventive concepts, the pinhole 1 r may be filled with therecovery layer 3 to cure or reduce the impact of defects, such as thepinhole 1 r, of the base layer 1. For example, as shown in FIG. 6, thesecond carbon atoms C2 contained in the recovery atomic layer Cln of therecovery layer 3 may be bonded to the first carbon atoms C1 contained inthe second atomic layer Alm, and as a result, hexagonal aromatic ringsmay be formed with an SP2 covalent bond structure. The dangling bonds DBof the pinhole 1 r may then be removed to prevent or reduce the impactof damage caused by hydrogen in a photolithography process. Accordingly,a photolithography process may be more reliably performed and thepellicle 50 may increase in lifespan or durability. The recovery atomiclayer Cln may partially have an SP3 covalent bond structure in thepinhole 1 r.

In some example embodiments, because the pellicle 50 for a photomaskincludes the recovery layer 3 containing atoms with a structure similarto that of the base layer 1 or because the recovery layer 3 has a carbonbond structure identical or similar to that of the base layer 1 orgraphene, the pellicle 50 may have optical, physical, and/or chemicalcharacteristics similar to those of the base layer 1.

FIG. 7 illustrates a flow chart showing a method of fabricating apellicle for a photomask, according to some example embodiments ofinventive concepts. FIGS. 8 and 10 illustrate cross-sectional viewsshowing a method of fabricating a pellicle for a photomask, according tosome example embodiments of inventive concepts. FIG. 9 illustrates anenlarged view showing section P2 of FIG. 8. FIG. 11 illustrates anenlarged view showing section P3 of FIG. 10. FIG. 12 illustrates aperspective view showing a step in a method of fabricating a pelliclefor a photomask, according to some example embodiments of inventiveconcepts.

Referring to FIGS. 7 to 9, a first carbon-containing material may beprovided to form a base layer 1 including a pinhole 1 r (S10). The baselayer 1 may be formed using a deposition process, such as thermalchemical vapor deposition (CVD), plasma enhanced chemical vapordeposition (PECVD), microwave enhanced chemical vapor deposition(MECVD), inductively coupled plasma chemical vapor deposition (ICPCVD),low pressure chemical vapor deposition (LPCVD), atomic layer deposition(ALD), chemical vapor deposition (CVD), and/or molecular layerdeposition (MLD). The plasma mentioned above may be generated by radiofrequency (RF), alternating current (AC) frequency, or direct current(DC) discharge. For example, a catalytic metal substrate 40 may beprovided thereon with vapor of the first carbon-containing material togrow a graphene or graphite thin layer. The catalytic metal substrate 40may primarily include a carbon-adsorptive transition metal, such asnickel, copper, iron, or cobalt, and further include noble metal, suchas gold, platinum, or silver. When the base layer 1 is formed by PECVDusing plasma, the PECVD may be performed at a relatively low processtemperature of about 300 to 700° C. When plasma is not used in adeposition process for forming the base layer 1, the catalytic metalsubstrate 40 or a chuck (not shown) that supports the catalytic metalsubstrate 40 may be under a temperature of about 1000° C. or higher. Thefirst carbon-containing material may be or may include, for example, atleast one of alkane, alkene, and alkyne each containing 1 to 10 carbonatoms. When carbon bonds in the first carbon-containing material arebroken during the deposition process, and then when the catalytic metalsubstrate 40 is provided on its surface with carbon atoms originatingfrom the broken carbon bonds, a graphene or graphite layer may be grownfrom the carbon atoms that are arranged to conform to the crystal planeof the surface of the catalytic metal substrate 40. The base layer 1 maybe formed to have a thickness of, for example, about 0.34 to 50 nm. Thebase layer 1 may include a plurality of base atomic layers Ala and Alm,and further include at least one pinhole 1 r on a surface thereof. Adescription of the base atomic layers Ala and Alm may be identical orsimilar to that discussed with reference to FIGS. 3 and 5. For example,as shown in FIG. 5, dangling bonds DB may be present in the pinhole 1 r.

Referring to FIGS. 7, 10, and 11, a second carbon-containing materialmay be coated on the base layer 1, filling the pinhole 1 r (S20). Thecoating of the second carbon-containing material may form a secondcarbon-containing material layer 3 c that not only fills the pinhole 1 rbut also covers a first surface 1 a of the base layer 1. The secondcarbon-containing material easily coat and sufficiently wet to the baselayer 1 to successfully fill the pinhole 1 r. After a heat treatmentprocess, the second carbon-containing material may decompose to form SP2covalent bonds with first carbon atoms (see C1 of FIG. 3) contained inthe base atomic layers Ala and Alm of the base layer 1. The secondcarbon-containing material may be or may include a polymer or a carboncompound containing at least one of carbon, nitrogen, oxygen, andhydrogen. The second carbon-containing material may be or may include,for example, catecholamine. The catecholamine may include dopamine (DA),polydopamine (PD), norepinephrine, or epinephrine. The catecholamine maybe a polymer of polyethyleneimine (PEI) and pyrogallol (PG). The secondcarbon-containing material may be at least one of fullerene, carbonblack, activated charcoal, charcoal, carbon nanoribbon, graphene quantumdots, graphene oxide, and nanodiamond. The second carbon-containingmaterial may exclude, i.e. may not include, an aromatic compound havingtwo or more benzene rings. The second carbon-containing material may beused alone or in the form of a solution with a solvent. Thecatecholamine may be formed by mixing and polymerizing polyethyleneimine(PEI) and pyrogallol (PG). Water may be used as the solvent.

As an example, a first solution may be prepared to includepolyethyleneimine (PEI), pyrogallol (PG), and water. The preparation ofthe first solution may be as follows. First, polyethyleneimine and watermay be mixed to prepare a first preliminary solution in which thepolyethyleneimine is dissolved in the water. The first preliminarysolution may have a polyethyleneimine concentration of about 1.25 to 20wt %. Next, the pyrogallol and the water may be mixed to prepare asecond preliminary solution in which the pyrogallol is dissolved in thewater. The second preliminary solution may have a pyrogallolconcentration of about 0.0125 to 0.2 M. The first solution may beprepared when the first preliminary solution and the second preliminarysolution are mixed at a volume ratio of 1:1. The first solution mayinclude catecholamine that is formed from the polymerization of thepolyethyleneimine and the pyrogallol. The first solution may be coatedon the base layer 1. A spin coating process may be employed to coat thefirst solution on the base layer 1. The spin coating process may beperformed, for example, at about 2,500 to 7,000 rpm for about 30 to 240seconds.

Referring to FIGS. 7, 1, and 2, after the second carbon-containingmaterial is coated, a heat treatment process may be performed at a firstprocess temperature to form a recovery layer 3 (S30). The first processtemperature may fall within a range, for example, from about 900° C. toabout 2,000° C. The heat treatment process may break bonds of carbonatoms with nitrogen, hydrogen, and oxygen atoms contained in the secondcarbon-containing material, such that the nitrogen, hydrogen, and oxygenatoms may be removed and remaining carbon atoms (corresponding to thesecond carbon atoms C2 of FIG. 4) may combine with the first carbonatoms (see C1 of FIG. 3) of the base layer 1, which may result in theformation of hexagonal aromatic rings. The base layer 1 may serve as aseed layer in the heat treatment process. The recovery layer 3 may havea thickness of about 0.5 to 10 nm. Through the processes above, apellicle membrane 20 may be formed to include the base layer 1 and therecovery layer 3. An inert gas, such as argon, may be supplied duringthe heat treatment process. Hydrogen may be additionally supplied duringthe heat treatment process. A flow amount ratio of argon to hydrogen maybe, for example, about 90:10 to 99:1.

The recovery layer 3 finally formed by the heat treatment process mayhave a chemical bond structure identical or similar to that discussedwith reference to FIGS. 2, 4, and 6. For example, a bond structurebetween carbon atoms contained in the recovery layer 3 may primarilyinclude SP2 covalent bonds, which are planar bond structures, andslightly include SP3 covalent bonds, which are tetrahedral bondstructures. A content/density of the SP2 covalent bonds between carbonatoms contained in the recovery layer 3 may be less than acontent/density of the SP2 covalent bonds between carbon atoms containedin the base layer 1. Nitrogen, hydrogen, and oxygen contained in thesecond carbon-containing material may not be completely removed duringthe heat treatment process, but may remain in the recovery layer 3. Therecovery layer 3 may then include at least one of nitrogen, hydrogen, oroxygen, or a sub-combination thereof, or a combination thereof. Acontent/density of nitrogen, hydrogen, and/or oxygen contained in therecovery layer 3 may be greater than a content/density of nitrogen,hydrogen, and/or oxygen contained in the base layer 1.

The pellicle membrane 20 may be separated from the catalytic metalsubstrate 40. The separation of the pellicle membrane 20 may beperformed in a first liquid. For example, the catalytic metal substrate40 on which the pellicle membrane 20 is formed may be provided into thefirst liquid, and then the pellicle membrane 20 may be separated fromthe catalytic metal substrate 40. The first liquid may be or mayinclude, for example, one of more of an iron chloride aqueous solution,an ammonium persulfate aqueous solution, a cerium ammonium nitrateaqueous solution, and a dimethylformamide aqueous solution. A rinseprocess using a second liquid may be additionally performed on theseparated pellicle membrane 20. The second liquid may include at leastone of deionized water, nitric acid, hydrochloric acid, acetic acid,hydrofluoric acid, aqua regia, ethyl alcohol, methyl alcohol, andisopropyl alcohol.

Referring to FIGS. 1 and 12, the separated pellicle membrane 20 may betranscribed onto a pellicle frame 30. This transcription process may beperformed in a third liquid 24. For example, the third liquid 24 may beprovided into a water tank 22, and the pellicle membrane 20 may befloated on the third liquid 24. The pellicle frame 30 may be elevatedfrom within the third liquid 24 and then attached to the pelliclemembrane 20. The third liquid 24 may be at least one of deionized waterand alcohol. The alcohol may include at least one of methyl alcohol,ethyl alcohol, and isopropyl alcohol. The pellicle frame 30 and thepellicle membrane 20 may be attached, e.g. directly attached, to eachother by, for example, a Van der Waals force without any glue materialbetween the pellicle frame 30 and the pellicle membrane 20. After that,the pellicle frame 30 and the pellicle membrane 20 may be dried.Alternatively, the pellicle membrane 20 may be attached to the pellicleframe 30 in a dry method performed at atmosphere or vacuum condition,not in the third liquid 24. At this stage, a heat treatment process maybe additionally performed or an adhesive may be used.

In some example embodiments, the recovery layer 3 may be used usingcatecholamine, which is easily coated on the base layer 1, with littleto no effort fills the pinhole or cavity 1 r, and is combined with thebase layer 1 to successfully form regular hexagonal aromatic rings. Assuch, a pellicle 50 for a photomask may be provided to increase surfaceuniformity of the pellicle membrane 20 and to have superior opticalcharacteristics, durability, and mechanical strength.

FIG. 13A illustrates an optical image of a base layer manufacturedaccording to some example embodiments of inventive concepts. FIG. 13Ashows that the pinhole 1 r is present on the base layer 1. The baselayer 1 may be a graphene or graphite thin layer. The base layer 1 mayhave a defect-free region (at a right upper side of FIG. 13A) on whichthe pinhole 1 r is absent and whose surface is relatively uniform andclean.

FIG. 13B illustrates an optical image obtained after coatingcatecholamine on the base layer of FIG. 13A. FIG. 13C illustrates anoptical image obtained after forming a recovery layer by thermallytreating the catecholamine of FIG. 13B. As shown in FIG. 13C, therecovery layer 3 has a uniform and clean surface and has no pinhole 1 r.FIG. 13C shows an image similar to that of the defect-free region onwhich the pinhole 1 r is absent as illustrated in FIG. 13A. The recoverylayer 3 may have a surface identical or similar to that of a graphene orgraphite thin layer having no defects such as the pinhole 1 r.

FIG. 14 illustrates a graph showing a first Raman spectrum A ofdefect-free graphite layer and a second Raman spectrum B of pelliclemembrane that is manufactured by a method of fabricating a pellicle fora photomask, according to some example embodiments of inventiveconcepts.

Referring to FIG. 14, the pellicle membrane 20 may have a second Ramanspectrum B whose intensity ratio of D peak to G peak, or D/G intensityratio, is about 0 to 1, or about 0.06 to 0.17. The G peak may appear atRaman shift of about 1580 cm⁻¹, arising from a vibration modecorresponding to stretching between carbon-to-carbon bonds having SP2covalent bond structures and providing information about whether or nothexagonal aromatic rings are included. The D peak may appear at Ramanshift of about 1340 to 1350 cm⁻¹, arising from defects such as carbonatoms having SP3 covalent bond structures and carbon vacancies. FIG. 14shows that carbon bonds in the pellicle membrane 20 may have relativelymore SP2 covalent bond structures than SP3 covalent bond structures.FIG. 14 also shows that the second Raman spectrum B of the pelliclemembrane 20 may have a similar shape to the first Raman spectrum A of adefect-free graphite thin layer. For example, each of the base layer 1and the recovery layer 3 included in the pellicle membrane 20 may have asimilar structure to that of a defect-free graphite thin layer.

The pellicle membrane 20 may have an absorption coefficient (orextinction coefficient) of about 0.01 or less, or about 0.0069 to 0.01,with respect to light whose wavelength is about 13.5 nm. The terms“absorption coefficient” or “extinction coefficient” may mean acoefficient that expresses a degree of reduction in amount of wavelength(light) or radiation when passing through a certain layer. Because thepellicle membrane 20 has an absorption coefficient (or extinctioncoefficient) of about 0.01 or less, the pellicle membrane 20 may not ormay absorb very little light. Accordingly, the pellicle membrane 20 maybe applicable to an EUV photolithography process, and may contribute tothe formation of ultra-fine patterns, e.g. ultrafine patterns used insemiconductor manufacturing.

The pellicle membrane 20 may have a tensile strength, for example, ofabout 200 MPa to about 3 GPa. The tensile strength of about 200 MPa toabout 3 GPa may refer to a tensile strength in a horizontal direction,for example, perpendicular to the C-axis direction of FIG. 2. In suchcases, the pellicle membrane 20 may be prevented or significantlyreduced from tears or wrinkles, which may result in a decrease inprocess failure.

FIG. 15 illustrates a cross-sectional view showing a pellicle for aphotomask, according to some example embodiments of inventive concepts.FIG. 16 illustrates an enlarged view showing section P4 of FIG. 15.

Referring to FIGS. 15 and 16, a pellicle 50 a for a photomask mayinclude a pellicle membrane 20 a that is further provided with a supportlayer 5 on the second surface 1 b of the base layer 1. The support layer5 may have a different crystal structure from that of the base layer 1.The base layer 1 may have a tensile strength in the C-axis directionless than a tensile strength in a thickness direction (e.g., the C-axisdirection) of the support layer 5. The support layer 5 may be or mayinclude, for example, at least one of diamond-like carbon (DLC) andcarbon nanotube. FIG. 16 shows an example in which the support layer 5is carbon nanotube. The carbon nanotube has a cylindrical shape, andthen has a tensile strength in the C-axis direction (e.g., in adirection perpendicular to a longitudinal direction of the carbonnanotube) greater than a tensile strength of a graphene or graphite thinlayer. Carbon bonds in the carbon nanotube may form SP2 covalent bondstructures to constitute regular hexagonal aromatic rings. The recoverylayer 3 and the base layer 1 may be identical or similar to thosediscussed with reference to FIGS. 1 to 6. A content/density of SP2covalent bonds between carbon atoms contained in the recovery layer 3may be less than a content/density of SP2 covalent bonds between carbonatoms contained in the support layer 5. A content/density of nitrogen,hydrogen, and/or oxygen contained in the recovery layer 3 may be greaterthan a content/density of nitrogen, hydrogen, and/or oxygen contained inthe support layer 5. The support layer 5 may include at least one ofiron, cobalt, and nickel.

The following describes a process of fabricating the pellicle membrane20 a of FIG. 15. As discussed with reference to FIGS. 7 to 11, the baselayer 1 and the recovery layer 3 may be formed. The base layer 1 and therecovery layer 3 may be separated from the catalytic metal substrate 40.The support layer 5 may be individually formed. When the support layer 5includes carbon nanotube, arc electric discharge, thermal deposition, orplasma deposition may be performed to form the support layer 5 on asecond catalytic metal substrate. The second catalytic metal substratemay be or may include at least one of iron, cobalt, and nickel. Thesupport layer 5 may be separated from the second catalytic metalsubstrate. At this stage, at least one of iron, cobalt, and nickelconstituting the second catalytic metal substrate may remain on thesupport layer 5. The support layer 5 may thus include at least one ofiron, cobalt, and nickel. The support layer 5 may be placed on thesecond surface 1 b of the base layer 1, and a heat treatment process maybe performed at a second process temperature. The second processtemperature may be less than the first process temperature discussedwith reference to FIG. 7. The second process temperature may fall withina range, for example, from about 100° C. to about 300° C. Alternatively,similarly to that discussed with reference to FIG. 12, the support layer5 and the base layer 1 may be attached to each other in a liquid. Inthis case, the support layer 5 and the base layer 1 may be combined witheach other by a Van der Waals force.

FIGS. 17 to 19 and 21 to 23 illustrate cross-sectional views showing apellicle for a photomask, according to some example embodiments ofinventive concepts. FIG. 20 illustrates an enlarged view showing sectionP5 of FIG. 19.

Referring to FIG. 17, a pellicle 50 b for a photomask may include apellicle membrane 20 b that is further provided with a capping layer 7on the recovery layer 3 of FIG. 15. The capping layer 7 may include atleast one of boron, boron carbide, and boron nitride. The capping layer7 may has a role to prevent or reduce the likelihood of reaction betweenhydrogen supplied in a photolithography process and a surface of one ofthe recovery layer 3 and the base layer 1. Other structural features maybe identical or similar to those discussed above with reference to FIG.15.

Referring to FIG. 18, a pellicle 50 c for a photomask may include apellicle membrane 20 c that is further provided with a first cappinglayer 7 a on the recovery layer 3 of FIG. 15 and a second capping layer7 b under the support layer 5 of FIG. 15. Each of the first and secondcapping layers 7 a and 7 b may include at least one of boron, boroncarbide, and boron nitride.

Alternatively, the support layer 5 may be excluded such that the secondcapping layer 7 b may be attached to, e.g. directly attached to, thesecond surface 1 b of the base layer 1.

Referring to FIGS. 19 and 20, a pellicle 50 d for a photomask mayinclude a pellicle membrane 20 d that is further provided with a secondrecovery layer 3 b between the base layer 1 and the support layer 5 ofFIG. 17. A first recovery layer 3 a of FIG. 18 may correspond to therecovery layer 3 of FIG. 17. A lower pinhole 1 rb may also be formed onthe second surface 1 b of the base layer 1. The base layer 1 may furtherinclude third base atomic layers Almb adjacent to the second surface 1b. The lower pinhole 1 rb may be formed in the third base atomic layersAlmb. The third base atomic layers Almb may have carbon bond structuresthat are identical or similar to those of the second base atomic layersAlm discussed with reference to FIG. 5. The second recovery layer 3 bmay fill the lower pinhole 1 rb. The second recovery layer 3 b may beidentical or similar to the recovery layer 3 discussed with reference toFIGS. 1 to 6. For example, the second recovery layer 3 b may includesecond recovery atomic layers Clnb. The second recovery atomic layersClnb may have carbon bond structures that are identical or similar tothose of the recovery atomic layers Cln discussed with reference to FIG.4. For example, the second recovery layer 3 b may cure defects such asthe lower pinhole 1 rb. A content/density of SP2 covalent bonds betweencarbon atoms contained in the second recovery layer 3 b may be less thana content/density of SP2 covalent bonds between carbon atoms containedin the base layer 1. A content/density of nitrogen, hydrogen, and/oroxygen contained in the second recovery layer 3 b may be greater than acontent/density of nitrogen, hydrogen, and/or oxygen contained in thebase layer 1. The formation of the second recovery layer 3 b may beidentical or similar to the formation of the recovery layer 3 discussedwith reference to FIG. 7.

Referring to FIG. 21, a pellicle 50 e for a photomask may include apellicle membrane 20 e that is further provided with a first cappinglayer 7 a on the first recovery layer 3 a of FIG. 19 and a secondcapping layer 7 b under the support layer 5 of FIG. 19. Other structuralfeatures may be identical or similar to those discussed above.

Referring to FIG. 22, a pellicle 50 f for a photomask may include apellicle membrane 20 f that differs from the pellicle membrane 20 e ofFIG. 21 in that the support layer 5 is interposed between the firstrecovery layer 3 a and the first capping layer 7 a, but not between thesecond recovery layer 3 b and the second capping layer 7 b. Otherstructural features may be identical or similar to those discussedabove.

Referring to FIG. 23, a pellicle 50 g for a photomask may include apellicle membrane 20 g in which the first recovery layer 3 a and thefirst capping layer 7 a are sequentially stacked on the first surface 1a of the base layer 1. The pellicle membrane 20 g may further include asecond base layer 10. The second surface 1 b of the base layer 1 may besequentially provided thereon with the support layer 5, the second baselayer 10, the second recovery layer 3 b, and the second capping layer 7b. The base layer 1 may be called a first base layer. Each of the firstand second base layers 1 and 10 may be identical or similar to the baselayer 1 discussed with reference to FIGS. 1 to 6.

FIG. 24 illustrates a cross-sectional view showing a pellicle accordingto some example embodiments of inventive concepts.

Referring to FIG. 24, a reticle 70 may include a photomask 60 to which,for example, the pellicle 50 of FIG. 1 is attached. The photomask 60 mayinclude a mask substrate 61 and a mask pattern 63 on the mask substrate61. Shape, size, and spacing of the mask pattern 63 may be merelyexamples and may variously be changed. The mask substrate 61 mayinclude, for example, quartz. The mask substrate 61 may include achromium nitride layer, a quartz layer, and/or a ruthenium cappinglayer. The quartz layer and the ruthenium capping layer may be providedtherebetween with molybdenum layers and silicon layers that arealternately and repeatedly stacked. The mask pattern 63 may include atantalum-based absorber and an antireflection layer on the absorber.

FIG. 24 shows that the reticle 70 includes the pellicle 50 of FIG. 1,but the reticle 70 may include, instead of the pellicle 50, any one ofthe pellicles 50 a to 50 g discussed with reference to FIGS. 15, 17 to19, and 21 to 23.

FIG. 25 illustrates a schematic diagram showing a photolithographyprocess that uses a reticle including a pellicle according to someexample embodiments of inventive concepts.

Referring to FIG. 25, according to some example embodiments of inventiveconcepts, a reflective photolithography process may be performed. In thereflective photolithography process, the reticle 70 having the pellicle50 attached thereto may be downwardly loaded on a reticle stage 140 of areflective photolithography system 100 that includes a light source 110,an illumination mirror system 120, a blinder 160, a projection mirrorsystem 170, and a wafer stage 180 in addition to the reticle stage 140.

The light source 110 may generate extreme ultraviolet (EUV) radiation. Alight whose wavelength is about 13.5 nm, for example, extremeultraviolet (EUV) radiation, may be generated from the light source 110using plasma that is produced when a carbon dioxide laser is irradiatedonto a small amount of tin (Sn) droplets. The light source 110 mayinclude a light collector 115. The light collector 115 may collect theEUV radiation generated from the light source 110, and may control theEUV radiation to move in a certain single direction. The EUV radiationgenerated from the light source 110 may pass through the light collector115, and may then be irradiated on the illumination mirror system 120.

The illumination mirror system 120 may include a plurality ofillumination mirrors 121, 122, 123, and 124. The illumination mirrors121 to 124 may be configured to condense the EUV radiation such that theEUV radiation may be prevented or reduced in likelihood from being lostout of mirrored irradiation pathways. The illumination mirrors 121 to124 may also be configured to control the EUV radiation to have overalluniform intensity distribution. Therefore, each of the illuminationmirrors 121 to 124 may include an concave or convex mirror to variouslychange the pathway of the EUV radiation. The illumination mirror system120 may shape the EUV radiation into a square-, circular-, or bar-shapedEUV radiation, which may be transferred to the reticle stage 140.

The reticle stage 140 may load the reticle 70 on a bottom surface andmove in a horizontal direction. For example, the reticle stage 140 maymove along an arrow direction shown in FIG. 25. The reticle stage 140may include an electrostatic chuck (ESC). The reticle 70 may be placedon the bottom surface of the reticle stage 140 so that a mask-patternside of the reticle 70 may face downwardly.

The blinder 160 may be under the reticle stage 140. The blinder 160 mayinclude a slit 162 and a plate 164. The slit 162 may have an apertureshape. The slit 162 may shape the EUV radiation that is delivered fromthe illumination mirror system 120 to the reticle 70 on the reticlestage 140. The EUV radiation from the illumination mirror system 120 maypass through the slit 162, and may then be irradiated on the reticle 70on the reticle stage 140. The EUV radiation reflected from the reticle70 on the reticle stage 140 may pass through the slit 162 and travel tothe projection mirror system 170. The plate 164 may block the EUVradiation that is irradiated on a region other than the slit 162. Thus,the blinder 160 may allow a portion of the EUV radiation to pass throughthe slit 162, and may use the plate 164 to block another portion of theEUV radiation. The slit 162 may permit passing of the EUV radiation thatis reflected from the reticle 70 placed on the bottom surface of thereticle stage 140.

The projection mirror system 170 may receive the EUV radiation that hasbeen reflected from the reticle 70 and passed through the slit 162, andmay transmit the EUV radiation to a wafer 190 on the wafer stage 180.The projection mirror system 170 may include a plurality of projectionmirrors 171, 172, 173, 174, 175, and 176. The EUV radiation, which isincident on the wafer 190 by the projection mirrors 171 to 176, may haveinformation about virtual aerial images of optical patterns on thereticle 70. The EUV radiation irradiated on the wafer 190 may keep itsshape that is formed when passing through the slit 162. The plurality ofprojection mirrors 171 to 176 may correct various aberrations.

The wafer stage 180 may accommodate the wafer 190 and move in thehorizontal direction. For example, the wafer stage 180 may move along anarrow direction shown in FIG. 25. The wafer stage 180 may movesimultaneously with the reticle stage 140 in the same direction at aconstant rate. For example, the wafer stage 180 may move in astep-and-scan manner. The EUV radiation irradiated from the projectionmirror system 170 may have a focus that is located on a surface of thewafer 190. For example, the wafer 190 may be provided thereon with aphotoresist layer having a predetermined thickness, and the focus of theEUV radiation may be positioned inside the photoresist layer.

Referring to FIGS. 24 and 25, the pellicle 50 may protect the photomask60 from contamination caused by particles during the photolithographyprocess, and the formation of photoresist patterns may not be affectedeven when the pellicle 50 is stained on its surface with foreignsubstances by which the EUV radiation is out of focus.

When the photolithography process continues, the pellicle membrane 20may change in pressure and temperature. The pellicle membrane 20 maypartially bulge downwardly due to a variation in volume thereof. Adistance d1, e.g. a maximal distance between a normally flat bottomsurface of the pellicle membrane 20 and a maximally bulged bottomsurface of the pellicle membrane, 20 may be less than or equal to, forexample, about 500 μm.

During the photolithography process, a hydrogen gas may be supplied toremove defects (e.g., photoresist residues) adhered to surfaces of themirrors 121 to 124 and 171 to 176. In case that the pellicle membrane 20includes no recovery layer 3, the pellicle membrane 20 may suffer fromdamage caused when hydrogen atoms are bonded to the dangling bonds DB inthe pinhole 1 r. In some example embodiments of inventive concepts,because the pellicle membrane 20 includes the recovery layer 3 thatfills the pinhole 1 r, the pellicle membrane 20 may be free of, orreduced in, damage.

In FIG. 25, the pathways of the EUV radiation are conceptuallyillustrated to aid in clearly understanding inventive concepts.

According to some example embodiments of inventive concepts, a pelliclefor a photomask may include a recovery layer to cure or reduce theimpact of defects, such as pinhole or cavity, possibly present on a baselayer. The recovery layer may fill the pinhole or cavity such that itmay be possible to prevent or reduce the likelihood of the occurrence ofdangling bonds in the pinhole or cavity. The pellicle may then beprevented or reduced in likelihood of occurrence from damage due tohydrogen atoms during a photolithography process, and accordingly thephotolithography process may be more reliably performed and the pelliclemay increase in lifespan or durability.

Furthermore, as in the base layer, the recovery layer may include acarbon-containing layer and therefore have similar optical, physical,and chemical characteristics to those of the base layer.

In a method of fabricating a pellicle for a photomask, catecholamine maybe used to form the recovery layer, which catecholamine is easily coatedon the base layer, with little to no effort fills the pinhole or cavity,and is combined with the base layer to form aromatic rings. The pelliclefor a photomask may increase surface uniformity of a pellicle membraneand have improved or superior optical characteristics, durability, andmechanical strength.

Although the present invention has been described in connection with theembodiments of the present invention illustrated in the accompanyingdrawings, it will be understood to those of ordinary skill in the artthat various changes and modifications may be made without departingfrom the technical spirit and essential feature of the presentinvention. It therefore will be understood that the embodimentsdescribed above are just illustrative but not limitative in all aspects.

What is claimed is:
 1. A method of fabricating a pellicle for aphotomask, the method comprising: providing a pellicle membrane; andtranscribing the pellicle membrane onto a frame, wherein providing thepellicle membrane includes, forming a base layer having a first surfaceand a second surface facing the first surface, coating a firstcarbon-containing material on the first surface of the base layer, andperforming a first heat treatment process at a first process temperatureto form a first recovery layer that is bonded to the base layer, whereinthe first carbon-containing material includes a catecholamine.
 2. Themethod of claim 1, wherein providing the pellicle membrane furtherincludes: forming a support layer; providing the support layer on thesecond surface of the base layer; and performing a second heat treatmentprocess at a second process temperature to bond the support layer to thebase layer.
 3. The method of claim 2, wherein the first processtemperature is between 900 and 2,000° C., and the second processtemperature is between 100 and 300° C.
 4. The method of claim 1, whereinthe base layer includes one of graphene, graphite, or both graphene andgraphite, and a content of SP3 covalent bonds between carbon atomscontained in the first recovery layer greater than a content of SP3covalent bonds between carbon atoms contained in the base layer.
 5. Themethod of claim 1, wherein forming the base layer includes providingvapor of a second carbon-containing material to deposit carbon atoms ona catalytic metal substrate.
 6. The method of claim 1, wherein the baselayer includes a first pinhole on the first surface, wherein coating thefirst carbon-containing material includes filling the first pinhole withthe first carbon-containing material.
 7. The method of claim 6, whereinthe base layer further includes a second pinhole on the second surface,wherein providing the pellicle membrane further includes, coating athird carbon-containing material on the second surface of the base layerto fill the second pinhole with the third carbon-containing material,and performing a heat treatment process to form a second recovery layerbonded to the base layer, wherein the third carbon-containing materialincludes a catecholamine.